Gas laser transmitter

ABSTRACT

A laser oscillator comprises a discharge tube for exciting laser medium, at least a pair of mirrors disposed along an optical axis of laser light emitted by the laser gas excited inside the discharge tube, a laser gas passage connected with the discharge tube, laser gas circulation means for circulating the laser gas inside the laser gas passage, and heat control means for controlling heat generated in at least one of the mirrors and the laser gas circulation means.

TECHNICAL FIELD

[0001] The present invention relates to a laser oscillator provided withtemperature control means. In particular, the invention relates to thelaser oscillator with capability of controlling temperature of a mirrorand a laser gas circulating component.

BACKGROUND ART

[0002]FIG. 7 to FIG. 10C illustrate gas laser oscillators of the priorart. First, FIG. 7 shows an example of general structure of anaxial-flow type gas laser oscillator of the prior art. In FIG. 7,discharge tube 701 made of a dielectric material such as glass isprovided with electrodes 702 and 703 on the perimetric sides thereof.Electrodes 702 and 703 are connected to power supply 704. There isdischarge space 705 formed inside discharge tube 701 between electrodes702 and 703. Final stage mirror 706 having a surface of generally allreflection and output mirror 707 having a surface of partial reflectionare securely placed to both ends of discharge space 705, and theyconstitute an optical resonator. Final stage mirror 706 and outputmirror 707 are simply called mirrors. Arrow 709 represents a directionto which laser gas flows. The laser gas circulates inside the axial-flowtype gas laser oscillator at a pressure of approximately 100 to 200Torr. Heat exchangers 711 and 712 operate at all the time to lowertemperature rise of the laser gas. Blower unit 713 circulates the lasergas to produce a flow of approximately 100 m/sec. in discharge space705. Laser gas passage 710 and discharge tube 701 are connected withlaser gas ports 714.

[0003] The laser gas delivered by blower unit 713 passes through lasergas passage 710, and it is introduced into discharge tube 701 from lasergas port 714. Electrodes 702 and 703 generate electrical dischargeinside discharge space 705 under the above condition. The laser gasreceives energy of the electrical discharge, and it is excited indischarge space 705. The excited laser gas turns into a resonant mode bythe optical resonator composed of final stage mirror 706 and outputmirror 707, and laser beam 708 is output from output mirror 707. Thislaser beam 708 is used for laser beam machining and the like.

[0004]FIG. 8 shows a general structure of an optical bench portion ofthe axial-flow type laser oscillator of the prior art. Output mirror 807is held in position by output side mirror retainer 815 a, and finalstage mirror 806 is held in position by final-stage side mirror retainer815 b. Mirror retainers 815 a and 815 b are provided with cooling plates816 a and 816 b respectively, and coolant 817 keeps flowing throughcooling plates 816 a and 816 b to remove heat at all the time.Temperature of coolant 817 is approximately 18° C., and it is introducedinto the laser oscillator at a flow rate of approx. 100 l/min. fromcooling system 818 provided outside of the laser oscillator.

[0005] By the way, there are two states of operation of the laseroscillator when differentiated in a general sense. They are a state inwhich electrical discharge takes place inside discharge space 805 andanother state in which no electrical discharge is produced. It isgeneral practice to produce electrical discharge when laser beam needsto be generated, and the electrical discharge is ceased when the laserbeam is not needed.

[0006] The laser oscillator operates blower unit 813 to run continuouslyto keep circulation of the laser gas regardless of using or not usingthe laser beam, and it generates the electrical discharge each time whenit produces the laser beam. It operates blower unit 813 to circulate thelaser gas at all the time because it requires several tens of seconds torestart again once blower unit 813 is turned off. On the contrary, itrequires only about several tens of milliseconds to stop and to restartthe electrical discharge, which is an acceptable level for practical usewithout a problem.

[0007] Although most of the laser beam is reflected by or penetratethrough final stage mirror 806 and output mirror 807, a small portionchanges to heat due to absorption in them. Final stage mirror 806 andoutput mirror 807 generate heat when electrical discharge takes place,but they do not heat up when there is no electrical discharge becauselaser oscillation does not occur.

[0008] When heat is generated, they need to be cooled with coolant 817.In the actual practice, however, final stage mirror 806 and outputmirror 807 are cooled at all the time while the laser oscillator is inoperation regardless of generating or not generating the electricaldischarge, since the cooling operation itself is not a problem even whenthere is no heat.

[0009] However, a problem arises when the laser oscillator is used undersuch an environment as high temperature and high humidity that thecomponents being cooled collect dew condensation. While a small amountof dew condensation does not pose a problem for the regular components,it gives a serious problem for final stage mirror 806 and output mirror807. No dew condensation occurs on final stage mirror 806 and outputmirror 807 when they heat up in the presence of electrical discharge.However, they do collect dew condensation when there is no electricaldischarge to produce heat in them. The dew condensation, if formed onany of final stage mirror 806 and output mirror 807, increasesabsorption factor of the laser beam in the condensed area, which canresult in damage to the mirror, and reduction in laser output.

[0010]FIG. 9 shows a general structure of another example of theaxial-flow type gas laser oscillator of the prior art. Discharge tubes901 made of a dielectric material such as glass, electrodes 902 and 903provided on the perimetric sides of discharge tubes 901, power supplies904 connected to electrodes 902 and 903, discharge spaces 905 insidedischarge tubes 901 provided between electrodes 902 and 903, final stagemirror 906, output mirror 907, laser gas passage 910, heat exchanger911, another heat exchanger 912 and blower units 913 correspondrespectively to discharge tubes 801 made of a dielectric material suchas glass, electrodes 802 and 803 provided on the perimetric sides ofdischarge tubes 801, power supply 804 connected to electrodes 802 and803, discharge spaces 805 inside discharge tubes 801 provided betweenelectrodes 802 and 803, final stage mirror 806, output mirror 807, lasergas passage 810, heat exchanger 811, another heat exchanger 812 andblower units 813 shown in FIG. 8. In addition, a direction of laser beam908 and flow direction 909 of laser gas also correspond to a directionof laser beam 708 and direction 709 of the laser gas in FIG. 7respectively.

[0011] Blower unit 913 produces a gas flow of approximately 100 m/sec indischarge spaces 905. Inverter 913 a controls a driving frequency forrotation of a propelling wheel of blower unit 913.

[0012] Laser gas deteriorates over time because it is dissociated by theelectrical discharge. Therefore, gas discharge mechanism 915 dischargesa certain amount of the laser gas at all times from laser gas passage910, and gas supply mechanism 916 continues to supply fresh laser gasfrom the outside to replace the amount of discharged gas. A gas pressureinside the laser gas supply passage is monitored at all the time withgas pressure sensor 917. Gas pressure sensor 917, gas dischargemechanism 915 and gas supply mechanism 916 are connected to gas pressurecontroller 918. Gas pressure controller 918 maintains the gas pressurein the laser gas passage constant at all the time by controlling gasdischarge mechanism 915 and gas supply mechanism 916.

[0013] However, conventional axial-flow type gas laser oscillator of thekind described above has problems, which will be discussed hereinafter.

[0014]FIG. 10A through FIG. 10C show electric current characteristics ofan ordinary type motor used in any of blower units 713, 813 and 913.

[0015]FIG. 10A shows a relation between temperature of gas suctionedinto any of blower units 713, 813 and 913 and electric current to themotor. Abscissa 1001 represents temperature of the gas suctioned intoblower units 713, 813 and 913, and ordinate 1002 represents the electriccurrent that flows to the motor. Line 1003 shows the relation betweenthem.

[0016] As is obvious from FIG. 10A, the lower the temperature of the gassuctioned into blower units 713, 813 and 913, the larger the currentdrawn by the motor of blower units 713, 813 and 913. This is because amass per unit volume of the gas increases with decrease in temperatureof the gas, which increases both the mass and flow rate of the gasdelivered per each time period from blower units 713, 813 and 913, whichhence increases workload of the motor.

[0017]FIG. 10B shows a relation between pressure of the gas suctioned inblower units 713, 813 and 913 and electric current to the motor.Abscissa 1011 represents pressure of the gas suctioned into blower units713, 813 and 913, ordinate 1012 represents the electric current thatflows to the motor, and line 1013 represents the relation between them.

[0018] As shown in FIG. 10B, the higher the gas pressure to blower units713, 813 and 913, the larger the electric current drawn by the motor. Areason of this is that a mass per unit volume of the gas increases withincrease in gas pressure, which increases both the mass and flow rate ofthe gas delivered per each time period from blower units 713, 813 and913, and it hence increases workload of the motor.

[0019]FIG. 10C shows a relation between driving frequency and electriccurrent to the motor of blower units 713, 813 and 913. Abscissa 1021represents the driving frequency of blower units 713, 813 and 913,ordinate 1022 represents the electric current to the motor, and line1023 represents the relation between them.

[0020] As is apparent from FIG. 10C, the higher the driving frequency ofblower units 713, 813 and 913, the faster the rotating speed of apropelling wheel in blower units 713, 813 and 913, and thereby thegreater the workload to the motor, which also increases the currentdrawn by the motor.

[0021] In general, increase in the motor current of blower units 713,813 and 913 increases heat generated in the motor, which results intemperature rise of the motor. In light of the long-term reliability, itis desirable to use a blower unit with as low an amount of motor currentas practically possible, since high temperature of the motor acceleratespartial deterioration of a motor coil and the like if used continuouslyfor a long period of time.

[0022] Normally, the gas pressure inside laser gas passages 710, 810 and910 is regulated to a predetermined pressure (e.g., approx. 20 kPa)within a range, which can provide an optimum mass and flow rate of thegas while restricting an increase in the amount of current that flows tothe motor of blower units 713, 813 and 913. In addition, temperature ofthe gas suctioned into blower units 713, 813 and 913 is controlled to beabout 40 to 50° C. under the normal operating condition, inconsideration of balancing between temperature of the laser gas heatedduring compression by blower units 713, 813 and 913 and heating by theelectrical discharge, and cooling capacities of heat exchangers 711,712, 811, 812, 911 and 912.

[0023] Problems are not anticipated so long as blower units 713, 813 and913 are operated under the above condition at all the time, since theamount of current to the motor is restricted to a certain limit orbelow, approx. 36 amperes or less for instance. However, another problemcomes up in a situation where temperature around the gas laseroscillator decreases in winter or for other reasons. In most cases, thegas laser oscillator is operated only in the daytime, while it is keptnot operational during the night hours. The ambient temperature goesdown to 5 to 10° C., for instance, when the laser oscillator is notoperating during the nighttime in winter. Therefore, temperature of thelaser gas inside the gas laser oscillator also goes down to as low atemperature as about 5 to 10° C. by the time the gas laser oscillator isstarted in the morning. When blower units 713, 813 and 913 are drivenunder this condition, an amount of current to the motor goes uptemporarily to approx. 40 A as compared to the regular level of about 36A, because temperature of the gas being suctioned in blower units 713,813 and 913 is low.

[0024] In reviewing further detail pertaining to temperature control ofthe gas suctioned in blower units 713, 813 and 913, it is a generalpractice that the gas temperature is controlled for cooling only, simplywith heat exchangers 711, 712, 811, 812, 911 and 912. Any of heatexchangers 711, 712, 811, 812, 911 and 912 exchanges heat between thegas and cooling water brought in from the outside. Since temperature ofthe cooling water introduced from the outside is generally in theneighborhood of 15 to 20° C., it can cool the gas having temperatureabove 15 to 20° C. However, it cannot heat the gas if the temperature isabout 5 to 10° C. In the normal operating condition, the gas temperatureeventually settles to an expected level of approx. 40 to 50° C. within10 to 20 minutes even if the gas laser oscillator is started in the lowtemperature condition with its gas temperature at around 5 to 10° C.,because the gas is heated by the heat generated by electrical dischargeand compression of the gas by blower units 713, 813 and 913, and thetemperature of the motor of blower units 713, 813 and 913 decreases intoa normal state without problem. However, the blower unit is operatedwith the motor consuming a larger current than the anticipated level fora period of about 10 to 20 minutes immediately after the start-up. Whenthe gas laser oscillator is operated everyday in this manner, partialdeterioration of motor coils and the like advances in blower units 713,813 and 913, which consequently leads to a loss of reliability in thelong-term use.

DISCLOSURE OF THE INVENTION

[0025] A laser oscillator comprises a discharge tube for exciting lasermedium, at least a pair of mirrors disposed along an optical axis oflaser light emitted by the laser medium excited in the discharge tube, alaser gas passage connected with the discharge tube, laser gascirculation means for circulating the laser gas in the laser gas passageand heat control means for responsively controlling heat generated in atleast one of the mirrors and the laser gas circulation means.

BRIEF DESCRIPTON OF THE DRAWINGS

[0026]FIG. 1 is a structural diagram of a laser oscillator according toa first exemplary embodiment of the present invention.

[0027]FIG. 2 is a structural diagram of a laser oscillator according toa second exemplary embodiment of the invention.

[0028]FIG. 3 is a structural diagram of a laser oscillator according toa third exemplary embodiment of the invention.

[0029]FIG. 4 is a structural diagram of a laser oscillator according toa fourth exemplary embodiment of the invention.

[0030]FIG. 5 is a sequence chart for controlling a gas pressureaccording to temperature of gas being suctioned into a blower unit ofthe laser oscillator shown in FIG. 4.

[0031]FIG. 6 is a sequence chart for responsively controlling a drivingfrequency of a blower unit according to temperature of gas beingsuctioned into the blower unit in a laser oscillator of a fifthexemplary embodiment of the invention.

[0032]FIG. 7 is a general structural diagram of a gas laser oscillatorof the prior art;

[0033]FIG. 8 is a general structural diagram of an optical bench portionof the laser oscillator of the prior art.

[0034]FIG. 9 is a general structural diagram of an axial-flow type gaslaser oscillator of the prior art.

[0035]FIG. 10A is a graphical chart showing an electric currentcharacteristic of a motor in a commonly used blower unit.

[0036]FIG. 10B is a graphical chart showing other electric currentcharacteristic of the motor in the commonly used blower unit.

[0037]FIG. 10C is a graphical chart showing still other electric currentcharacteristic of the motor in the commonly used blower unit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Exemplary Embodiment

[0038]FIG. 1 shows a structure of a laser oscillator according to thefirst exemplary embodiment of this invention.

[0039] In FIG. 1, discharge tubes 101 made of dielectric material suchas glass are provided with electrodes 102 and 103 on the perimetricsides thereof Electrodes 102 and 103 are connected to power supplies104. There are discharge spaces 105 formed inside discharge tubes 101between electrodes 102 and 103. Final stage mirror 106 having a surfaceof generally all reflection and output mirror 107 having a surface ofpartial reflection are securely placed to two ends of discharge spaces705, and they constitute an optical resonator. Laser beam 108 is outputfrom output mirror 107. Laser gas circulates inside the gas laseroscillator. Heat exchangers 111 and 112 responsively function to controltemperature of the laser gas. Blower unit 113 circulates the laser gas.Laser gas passage 110 and discharge tubes 101 are connected with lasergas ports 114.

[0040] The laser gas delivered by blower unit 113 passes through lasergas passage 110, and it is introduced into one of discharge tubes 101from laser gas port 114. Electrodes 102 and 103 generate electricaldischarge in discharge spaces 105 under the above condition. The lasergas receives energy of the electrical discharge, and it is excitedinside discharge space 705. The excited laser gas turns into a resonantmode by the optical resonator composed of final stage mirror 106 andoutput mirror 107, and laser beam 108 is output from output mirror 107.This laser beam 108 is used for laser beam machining and the like.

[0041] Output mirror 107 is held in position by output side mirrorretainer 115 a, and final stage mirror 106 is held in position by finalstage side mirror retainer 115 b. Output mirror 107 and final stagemirror 106 generate heat therein due to reflection and penetration ofthe laser beam. Output side mirror retainer 115 a and final stage sidemirror retainer 115 b are provided with cooling plates 116 a and 116 b,and coolant 117 flows through cooling plates 116 a and 116 b toresponsively remove the heat.

[0042] Coolant 117 is introduced into the laser oscillator at atemperature of approx. 18° C. and a flow rate of approx. 100 l/min fromcooling system 118 provided outside of the laser oscillator. Coolant 117exchanges heat with a number of components in the laser oscillator,including cooling plates 116 a and 116 b, heat exchangers 111 and 112,blower unit 113, and so on, and it is returned again into cooling system118 after the temperature goes up to approx. 20° C.

[0043] Coolant 117 is cooled down to about 18° C. in cooling system 118,and introduced again into the laser oscillator. Coolant passage 119leading to cooling plates 116 a and 116 b is provided with solenoidvalve 120, of which operation is controlled by controller 121.

[0044] The laser oscillator operates in a manner as describedhereinafter. When the laser oscillator is activated, blower unit 113starts operating, and the laser gas begins circulating. Electricaldischarge can be initiated in this state to produce laser oscillation.While the coolant is introduced from cooling system 118 into circulationthrough the laser oscillator in this state, final stage mirror 106 andoutput mirror 107 are not cooled at this stage because solenoid valve120 provided in coolant passage 119 to cooling plates 116 a and 116 bremains closed.

[0045] Electrical discharge is now generated to produce a laser beam.Generation of the electrical discharge is controlled by controller 121.Controller 121 opens solenoid valve 120 at the same time with generationof the electrical discharge, to let coolant 117 start flowing towardcooling plates 116 a and 116 b. When the electrical discharge issuspended, controller 121 closes solenoid valve 120 to stop the flow ofcoolant 117 to cooling plates 116 a and 116 b. However, coolant 17continues flowing to the components other than cooling plates 116 a and116 b regardless of generating or not generating the electricaldischarge.

[0046] With the structure as discussed above, final stage mirror 106 andoutput mirror 107 are cooled only when the electrical discharge takesplace, or the laser is oscillating. They are thus cooled responsivelyand the temperature controlled responsively only when the cooling isneeded. When the mirrors are cooled in an absence of electricaldischarge under the environment of high temperature and high humidity,the mirrors produce dew condensation, which can be a cause of problemssuch as decrease in laser output due to damage to the mirrors. Such dewcondensation does not occur in the structure of this exemplaryembodiment.

[0047] It may be considered to raise temperature of the coolant as analternative measures to prevent dew condensation. As a conceivableexample, the temperature of the coolant at the normal level of 18° C.may be raised to 25° C. However, the raise in temperature of the coolantresults in a lowering of efficiency of heat exchangers 111 and 112, andconsequent increase in the laser gas temperature. On the principle oflaser oscillation, increase in the laser gas temperature lowersefficiency of the laser oscillation and laser output. It is thereforenot appropriate to raise the temperature of the coolant.

[0048] There is another method, as has been tried in the past, in whicha heater or the like is used to regulate temperature of only the coolantthat flows to the mirrors in a manner to maintain it at a temperatureabove a dew point of the surrounding air. However, such a structurerequires sensors for detecting the temperature and humidity as well as atemperature regulator, which increases a number of components and makesthe structure complex, and it is therefore not considered practical. Onthe contrary, this exemplary embodiment can be considered superior bothin cost and in reliability, since it is quite simple in its structureand operating principle without requiring such components as a sensorand new components.

Second Exemplary Embodiment

[0049]FIG. 2 shows a structure of a laser oscillator according to thesecond exemplary embodiment of this invention.

[0050] In FIG. 2, power supplies 204, final stage mirror 206, outputmirror 207, laser gas passage 210, heat exchangers 211 and 212, blowerunit 213, laser gas ports 214, output side mirror retainer 215 a, finalstage side mirror retainer 215 b, cooling plates 216 a and 216 b,coolant 217, cooling system 218, coolant passage 219, solenoid valve 220and controller 221 correspond analogously to power supplies 104, finalstage mirror 106, output mirror 107, laser gas passage 110, heatexchangers 111 and 112, blower unit 113, laser gas ports 114, outputside mirror retainer 115 a, final stage side mirror retainer 115 b,cooling plates 116 a and 116 b, coolant 117, cooling system 118, coolantpassage 119, solenoid valve 120 and controller 121 shown in FIG. 1,respectively. Details of the individual components are thereforeskipped.

[0051] This second exemplary embodiment differs from the first exemplaryembodiment in a respect that heat in the mirrors can be cooledsufficiently by natural heat dissipation to the surrounding air when thelaser oscillator is used by generating electrical discharge with areduced power, that is, an output power of the laser is reduced to a lowlevel, since the heat generated in the mirrors is small. It is not evennecessary in such a case to circulate the coolant for cooling down. Itis more important to avoid the possibility of dew condensation withoutcirculating the coolant.

[0052] In the structure of FIG. 2, therefore, temperature detectionmeans 222 such as a thermistor disposed to output side mirror retainer215 a monitors a temperature, and flow control means lets coolant 217flow only when the temperature reaches a predetermined value, to controlcooling and hence temperature of output side mirror retainer 215 a andfinal stage side mirror retainer 215 b responsively. Although the secondexemplary embodiment shown in FIG. 2 requires the temperature detectionmeans as compared to the first exemplary embodiment, it is stillsuperior in both cost and reliability, since it does not require atemperature regulator of the type discussed in the example of the priorart.

Third Exemplary Embodiment

[0053]FIG. 3 shows a structure of a laser oscillator according to thethird exemplary embodiment of this invention.

[0054] In FIG. 3, power supplies 304, final stage mirror 306, outputmirror 307, laser gas passage 310, heat exchangers 311 and 312, blowerunit 313, laser gas ports 314, output side mirror retainer 315 a, finalstage side mirror retainer 315 b, cooling plates 316 a and 316 b,coolant 317, cooling system 318, coolant passage 319, solenoid valve 320and controller 321 correspond analogously to power supplies 104, finalstage mirror 106, output mirror 107, laser gas passage 110, heatexchangers 111 and 112, blower unit 113, laser gas ports 114, outputside mirror retainer 115 a, final stage side mirror retainer 115 b,cooling plates 116 a and 116 b, coolant 117, cooling system 118, coolantpassage 119, solenoid valve 120 and controller 121 shown in FIG. 1,respectively. Details of the individual components are thereforeskipped.

[0055] This third exemplary embodiment differs from the first and thesecond exemplary embodiments in a respect that humidity detection means323 are used to monitor dew points of the air around output side mirrorretainer 315 a and final stage side mirror retainer 315 b, andtemperature control is performed in a responsive manner by reducing aflow rate of coolant 317 and the like if there is a risk of dewcondensation. In the structure of FIG. 3, although humidity detectionmeans 323 such as a humidity sensor is needed, it is still superior inboth cost and reliability, since it does not require a temperatureregulator of the type discussed in the example of the prior art.

[0056] Any of the first through the third exemplary embodimentsdiscussed above provides the laser oscillator which is superior inrespects of the cost and reliability, capable of preventing dewcondensation on the mirrors with their simple structures, and producessteady laser output at all the time.

Fourth Exemplary Embodiment

[0057]FIG. 4 is a structural diagram of a laser oscillator according tothe fourth exemplary embodiment of this invention.

[0058] In FIG. 4, discharge tubes 401, electrodes 402 and 403, powersupplies 404, discharge spaces 405, final stage mirror 406, outputmirror 407, laser beam 408, laser gas passage 410, heat exchangers 411and 412, blower unit 413 and laser gas ports 414 are analogous todischarge tubes 101, electrodes 102 and 103, power supplies 104,discharge spaces 105, final stage mirror 106, output mirror 107, laserbeam 108, laser gas passage 110, heat exchangers 111 and 112, blowerunit 113 and laser gas ports 114 shown in FIG. 1 respectively. Detailsof the individual components are therefore skipped.

[0059] Inverter 413 a controls a driving frequency for rotation of apropelling wheel of blower unit 413. Arrow 409 represents a direction ofthe laser gas delivered by blower unit 413.

[0060] Laser gas deteriorates over time because it is dissociated byelectrical discharge. Therefore, gas discharge mechanism 415 adaptivelydischarges a certain amount of the laser gas from laser gas passage 410,and gas supply mechanism 416 adaptively supplies fresh laser gas fromthe outside to replace the amount of discharged gas. A gas pressureinside the laser gas supply passage is monitored at all the time withgas pressure sensor 417. Gas pressure sensor 417, gas dischargemechanism 415 and gas supply mechanism 416 are connected to gas pressurecontroller 418. Gas pressure controller 418 maintains the gas pressurein the laser gas passage 410 constant at all the time by controlling gasdischarge mechanism 415 and gas supply mechanism 416 in a responsivemanner.

[0061] Blower unit 413 is provided with temperature sensor 419 at asuction side thereof to measure a temperature of the gas to besuctioned, and this temperature sensor 419 is connected to gas pressurecontroller 418.

[0062] Since a pressure and temperature of the laser gas are maintainedin this manner, heat generated during operation of the blower unit fordelivery of the laser gas is controlled responsively, to achieveresponsive temperature control.

[0063]FIG. 5 is a flowchart showing an operation sequence of thestructure shown in FIG. 4.

[0064] First, a temperature of the gas suctioned into blower unit 413 ismeasured in the step 501, and the measured temperature is judged in thestep 502 as to whether it is above or below a predetermined temperature(e.g., 40° C.). Temperature sensor 419 keeps monitoring the temperatureof the gas suctioned in blower unit 413 at all the time from thestart-up of the laser oscillator. Assume that the gas laser oscillatoris started in a winter morning, for example. Temperature of the lasergas inside the gas laser oscillator may be as low as about 5 to 10° C.when the gas laser oscillator is started, and temperature sensor 419detects this temperature.

[0065] When the temperature of the gas suctioned into blower unit 413 isjudged to be equal to or above the predetermined temperature (e.g., 40°C.) in the step 502, the process goes on to the step 503. In the step503, the gas laser oscillator is operated with a pressure of the gassuctioned into blower unit 413 at the regular value (e.g., 20 kPa).

[0066] If the temperature of the gas suctioned into blower unit 413 isjudged below the predetermined temperature (e.g., 40° C.) in the step502, the process goes on to the step 504. In the step 504, the pressureof the gas suctioned into blower unit 413 is regulated to a low level(e.g., 18.7 kPa). Gas pressure controller 418 receives temperatureinformation from temperature sensor 419, and lowers the regulating valueof the gas pressure automatically by approx. 1.3 kPa. In other words,the pressure of the gas suctioned into blower unit 413 is normally inthe neighborhood of 20 kPa, and this value is lowered to about 18.7 kPa.Temperature of the suctioned gas has fallen to 5 to 10° C. here,although it normally is 40 to 50° C. If blower unit 413 is driven underthis condition, the current drawn by the motor increases undoubtedly,because the gas temperature is so low. For instance, although the normalelectric current is about 36 A, it increases to approx. 40 A due to thelow temperature of the suctioned gas. Since the pressure of thesuctioned gas is lowered to 18.7 kPa from the normal value of 20 kPa, inthe embodied structure of FIG. 4, the load of the motor is balanced, andthe motor current is maintained consequently to the normal value ofapprox. 36 A.

[0067] The process is then goes back again to the step 501 from the step503 or the step 504, and temperature of the gas suctioned into blowerunit 413 is measured again. Operation of the gas laser oscillator iscontinued even when the process goes on through the step 504, and theprocess eventually advances to the step 503 when the temperature of thegas suctioned into blower unit 413 rises gradually and exceeds thepredetermined value (e.g., 40° C.). The gas pressure inside laser gaspassage 410 is then brought back to the normal value (e.g., 20 kPa) inthe step 503.

[0068] The laser gas oscillator operated in this manner can maintain theelectric current to the motor below a certain value at all the time evenunder such a condition as an early start-up in the morning of winter daywhich is likely to increase the current to the motor of blower unit 413.The load of the motor is regulated in this manner to responsivelycontrol the temperature affected by heat generated therein. As a result,this invention reduces deterioration of the motor componentsattributable to temperature rise of the motor, thereby providing thelaser gas oscillator with high reliability for a prolonged time.

[0069] A matter of concern here is that a laser output decreases whengas pressure in laser gas passage 410 is reduced. A reduction in gaspressure inside of laser gas passage 410 means reduction in gas pressurein discharge space 405, which leads to decrease in both mass and flowrate of the laser gas that circulates through discharge space 405. Sincean output of laser beam 408 produced by the laser oscillator changes inproportion to the mass and flow rate of the laser gas flowing throughdischarge space 405, the laser output decreases as the gas pressuredecrease. However, the laser oscillator has such a characteristic thatan efficiency of laser oscillation increases, and hence the laser outputincreases, when temperature of the laser gas decreases, according to theprinciple of laser oscillation. That is, the laser output has a tendencyof decreasing if the gas pressure is lowered. On the other hand, sincethe laser oscillation efficiency increases due to decrease intemperature of the laser gas, they consequently cancel with each other,to provide a characteristic of the laser output that hardly varies inpower from that of the normal condition.

Fifth Exemplary Embodiment

[0070]FIG. 6 is a sequence chart representing the fifth exemplaryembodiment of this invention, wherein a laser oscillator responsivelycontrols a driving frequency of blower unit 413 according to temperatureof gas suctioned into blower unit 413.

[0071] Because the step 601 and step 602 are analogous to thecorresponding steps 501 and 502 of FIG. 5 respectively, individualexplanation is not repeated here in detail.

[0072] When temperature of the gas suctioned into blower unit 413 isjudged equal to or above a predetermined temperature (e.g., 40° C.) inthe step 602, the process goes on to the step 603. In the step 603,blower unit 413 is operated with a normal driving frequency (e.g., 700Hz).

[0073] If the temperature of the gas suctioned into blower unit 413 isjudged below the predetermined temperature (e.g., 40° C.) in the step602, the process goes on to the step 604. In the step 604, the drivingfrequency of blower unit 413 is lowered, and operated with a frequencyof 650 Hz, for instance. Gas pressure controller 418 receivestemperature information from temperature sensor 419, and lowers thedriving frequency of blower unit 413 automatically by about 50 Hz. Inother words, the driving frequency of blower unit 413 is normally 700Hz, but this figure is lowered to approx. 650 Hz. Assuming that thelaser oscillator is started early in the morning of a winter day,temperature of the suctioned gas has fallen to 5 to 10° C., although itshould be normally 40 to 50° C. If blower unit 413 is driven under thiscondition, the current consumed by the motor increases because the gastemperature is so low. For instance, although the normal electriccurrent is about 36 A, it increases to approx. 40 A because of the lowtemperature of the suctioned gas. Since the driving frequency of blowerunit 413 is lowered to 650 Hz from the normal frequency of 700 Hz, inthe structure of FIG. 4, the load of the motor is balanced, and themotor current is maintained consequently to the normal value of approx.36 A.

[0074] The process is then goes back again to the step 601 from the step603 or the step 604, and temperature of the gas suctioned into blowerunit 413 is measured. Operation of the gas laser oscillator is continuedeven when the process goes on through the step 604, and the processeventually advances to the step 603 when the temperature of the gassuctioned into blower unit 413 rises gradually and exceeds thepredetermined value (e.g., 40° C.). The driving frequency of blower unit413 is then brought back to the normal frequency (e.g., 700 Hz).

[0075] The operation shown in FIG. 6 can thus maintain electric currentto the motor below a certain value at all the time even under such acondition as an early start-up in the morning of winter day that islikely to increase the current to the motor of blower unit. The load ofthe motor is regulated in this manner to responsively control thetemperature affected by heat generated therein. As a result, thisinvention reduces deterioration of the motor components attributable totemperature rise of the motor, thereby providing the laser gasoscillator with high reliability for a long period of time.

[0076] A matter of concern here is that a laser output decreases whenthe driving frequency of blower unit 413 is lowered. A low drivingfrequency of blower unit 413 means decrease in gas volume delivered byblower unit 413, which leads to decrease in both mass and flow rate ofthe laser gas that flows through discharge space 405. Since an output oflaser beam 408 produced by the laser oscillator varies in proportion tothe mass and flow rate of the laser gas flowing through discharge space405, the laser output decreases as the driving frequency of blower unit413 is lowered. However, the laser oscillator has such a characteristicthat an efficiency of laser oscillation increases, and hence the laseroutput increases, when temperature of the laser gas decreases, accordingto the principle of laser oscillation. That is, the laser output has atendency of decreasing if the driving frequency of blower unit 413 islowered. On the other hand, the laser oscillation efficiency increasesdue to decrease in temperature of the laser gas. In consequence, theycancel with each other, so as to provide a characteristic of the laseroutput that hardly varies in power from that of the normal condition.

[0077] As described explicitly, this fifth exemplary embodiment canprovide the gas laser oscillator with high reliability, which can beused steadily for a long period of time.

Industrial Applicability

[0078] A gas laser oscillator of this invention has capability ofcontrolling heat and temperature responsively by overcoming a variety oftroubles attributable to temperature changes, and providing highreliability for long term of steady operation.

1. A laser oscillator comprising: a discharge tube for exciting lasergas; at least a pair of mirrors disposed along an optical axis of laserlight emitted by the laser gas excited in said discharge tube; a lasergas passage in connection with said discharge tube; laser gascirculation means for circulating the laser gas in said laser gaspassage and said discharge tube; and heat control means for responsivelycontrolling heat generated in at least one of said mirrors and saidlaser gas circulation means.
 2. The laser oscillator according to claim1, wherein said heat control means comprises: at least a pair of mirrorretainers for retaining said pair of mirrors individually; a coolingelement for cooling any of said pair of mirror retainers; coolant incirculation through inside said cooling element; and flow rate controlmeans for controlling a flow rate of said coolant.
 3. The laseroscillator according to claim 2, wherein said flow rate control meansrestricts flow of said coolant when laser is not emitted.
 4. The laseroscillator according to one of claim 2 and claim 3, wherein said flowrate control means restricts flow of said coolant when heat is notgenerated in any of said pair of mirror retainers.
 5. The laseroscillator according to claim 4 further comprising temperature detectionmeans disposed to any of said pair of mirror retainers, wherein saidtemperature detection means detects temperature generated in any of saidpair of mirror retainers, and said flow rate control means restrictsflow of said coolant based on a result of detection by said temperaturedetection means.
 6. The laser oscillator according to one of claim 2through claim 5 further comprising humidity detection means disposed inthe vicinity of any of said pair of mirror retainers, wherein said flowrate control means restricts flow of said coolant when humidity is equalto or higher than a predetermined level.
 7. The gas laser oscillatoraccording to claim 1, wherein said laser gas circulation means isprovided with a blower unit disposed to said laser gas passage, and saidheat control means comprises a first temperature sensor for measuring atemperature of the laser gas suctioned by said blower unit, a gas supplymechanism for supplying laser gas into said laser gas passage, a gasdischarge mechanism for discharging the laser gas from said laser gaspassage, and gas pressure controlling means for controlling a pressureof the laser gas inside said laser gas passage based on a signal fromsaid first temperature sensor.
 8. The gas laser oscillator according toclaim 7, wherein said gas pressure controlling means comprises acontroller for controlling said supply mechanism and said dischargemechanism.
 9. The gas laser oscillator according to claim 1, whereinsaid laser gas circulation means is provided with a blower unit disposedto said laser gas passage, and said heat control means comprises asecond temperature sensor for measuring a temperature of the laser gassuctioned by said blower unit, and frequency control means forcontrolling a driving frequency of said blower unit based on a signalfrom said second temperature sensor.
 10. The gas laser oscillatoraccording to claim 9, wherein said frequency control means includes aninverter for controlling said blower unit.